The crystallization of proteins for structure-function studies and structure based drug design has become an increasingly important part of biotechnology research. When crystal growth is attempted for a new protein, the appropriate chemical conditions (i.e. protein concentration in solution, precipitate type and concentration, pH, and growth temperature) are unknown and have typically been determined by trial and error experimentation.
Typically 1000 or more different sets of crystal growth conditions are screened to determine conditions conducive to crystallization. The screening involves repetitive procedures that are extremely laborious and tedious. With present laboratory protein crystal growth equipment, each crystallization chamber requires about one micro-liter of protein solution. The protein solutions typically have concentrations in the range of 10 to 25 micrograms per microliter to facilitate crystal growth. Therefore, to screen 1000 samples typically requires between 10 and 25 milligrams of protein. This is a considerable and costly amount, especially for proteins that are difficult to isolate or generally express. A large percentage (about 50%) of the proteins cannot easily be expressed in milligram quantities.
Thus, it would be desirable to provide methods for screening protein crystal growth conditions that require picogram to microgram amounts of protein for each screening condition. Preferably such methods would require only picogram to nanogram amounts of protein in picoliter to nanoliter volumes in each screening condition sample.
It would be further desirable to provide high throughput screening methods for screening protein crystal growth conditions in a large number of samples on a sub-microgram scale. These methods would use a microarray as a platform for protein crystal growth. The methods would also utilize automatic dispensing of solutions and scoring of crystal growth.